Method and apparatus for interleaving in a wireless communication system

ABSTRACT

The method and apparatus in accordance with the present invention receives bits, writes the bits row-by-row in a matrix, reads the bits column-by-column from the matrix, groups and rotates the bits read column-by-column from the matrix so as to evenly separate the bits in position, frequency, space over one symbol period.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/701,478 filed Jul. 22, 2005, which is incorporated herein byreference.

FIELD OF THE INVENTION

This invention is generally related to wireless communication and morespecifically to interleaving.

BACKGROUND OF THE INVENTION

The wireless communications industry has experienced an explosive growthin the last decade. However, the available spectrum for wirelesscommunications has not grown at the same rate. Increased cost ofacquiring spectrum to accommodate users has resulted in an increasedinterest in spectrum efficient techniques that use multiple transmit andreceive antennas instead of the conventional single transmit and receiveantennas.

In conventional wireless communications, a single antenna is used at thesource and the destination. In some cases, this gives rise to problemswith multipath effects. When an electromagnetic field is met withobstructions such as hills, canyons, buildings, and utility wires, thewavefronts are scattered, and thus they take many paths to reach thedestination. The late arrival of scattered portions of the signal causesproblems such as fading, cut-out (cliff effect), and intermittentreception (picket fencing). In digital communications systems such aswireless internet, these problems can cause a reduction in data speedand an increase in the number of errors. The use of two or moreantennas, along with the transmission of multiple signals (one for eachantenna) at the source and the destination, can take advantage of themultipath wave propagation.

One of the most promising spectrum efficient techniques aremultiple-input, multiple-output (MIMO) systems. MIMO is an antennatechnology for wireless communications in which multiple antennas areused at both the source (transmitter) and the destination (receiver).The antennas at each end of the communications circuit are combined tominimize errors and optimize data speed. These systems exploit thespatial dimension to a larger extent than previous systems and have beenshown to be capable of supporting very high data rates withoutincreasing the bandwidth. MIMO is a reliable technique and has been putinto practice in production of WLANS. MIMO is one of several forms ofsmart antenna technology, the others being Multiple Input Single Output(MISO) and Single Input Multiple Output (SIMO). MIMO technology hasaroused interest because of its possible applications in digitaltelevision (DTV), WLANs, metropolitan area networks (MANs), and mobilecommunications.

What are needed, therefore, are methods and systems for more fullyutilizing multiple transmit and/or multiple receive paths.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to a method and apparatus forinterleaving bits in a multi-path wireless communications system. Theinvention comprises a method and apparatus for receiving bits, writingthe bits row-by-row in a matrix, reading the bits column-by-column fromthe matrix, and grouping and rotating the bits read from the matrix soas to separate the bits by position, frequency, and by streams, over onesymbol period.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed. Thedetailed description is not intended to limit the scope of the claimedinvention in any way.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1A is a block diagram of a SISO transmitter and receiver.

FIG. 1B is a block diagram of a SIMO transmitter and receiver.

FIG. 1C is a block diagram of a MISO transmitter and receiver.

FIG. 1D is a block diagram of a MIMO transmitter and receiver.

FIG. 2 is a frequency vs. Signal to Noise Ratio (SNR) graph of datapoints.

FIG. 3 is a frequency vs. SNR vs. number of streams graph of datapoints.

FIG. 4 is a block diagram of transmission and reception portions of awireless communication system.

FIG. 5 shows bits interleaved by a Quartenary Phase Shift Keying (QPSK)interleaver.

FIG. 6 illustrates results produced by a Quadrature Amplitude Modulation(QAM) interleaver.

FIG. 7 is a block diagram of an exemplary interleaver.

FIG. 8 is a diagram of a row-column interleaver.

FIG. 9 illustrates results produced by an interleaver for a two streamtransmission system.

FIG. 10 illustrates results produced by an interleaver for a threestream transmission system.

FIG. 11 is a block diagram of an exemplary computer system.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers mayindicate identical or functionally similar elements. Additionally, theleft-most digit(s) of a reference number may identify the drawing inwhich the reference number first appears.

DETAILED DESCRIPTION OF THE INVENTION

While the present invention is described herein with reference toillustrative embodiments for particular applications, it should beunderstood that the invention is not limited thereto. Those skilled inthe art with access to the teachings provided herein will recognizeadditional modifications, applications, and embodiments within the scopethereof and additional fields in which the invention would be ofsignificant utility.

The present invention will be described in terms of an embodimentapplicable to the pre-processing of encoded transmission data using aninterleaver. It will be understood that the essential pre-processingconcepts disclosed herein are applicable to a wide range of electronicsystems, architectures and hardware elements. Thus, although theinvention will be disclosed and described in terms of pre-processingtransmission data for a wireless system to increase transmissionreliability, the invention is not limited to this field.

Interleaving is a key component of many digital communication systemsinvolving forward error correction (FEC) coding. Interleaving encodedsymbols provides a form of time and/or frequency diversity to guardagainst localized corruption or bursts of errors. The role ofinterleaving is to randomize the bits, so that error events due to deepchannel fades are maximally de-correlated. If the interleaver hassufficient depth the fading processes that affect successive symbolsbelonging to the same codeword will be uncorrelated. Therefore, from theperspective of any single codeword, interleaving makes a burst errorchannel appear as one which has only random errors.

In the Institute of Electrical and Electronics Engineers (IEEE) 802.11astandard, a block interleaver is specified where encoded bits in oneOrthogonal Frequency Division Multiplexed (OFDM) symbol are uniformlypermuted across all bit positions in the constellation. The IEEEwireless LAN standards 802.11a, 802.11g and Hiperlan/2 are all OFDMbased and use 48 data sub-carriers and 4 pilot tones. They also use thesame interleaving scheme. The interleaving scheme is defined by twopermutations. The first permutation ensures that adjacent bits aremodulated onto nonadjacent sub-carriers and the second permutationensures that that adjacent bits are mapped alternatively onto less andmore significant bits of the constellation.

The type of interleaving chosen for a transmission system is a functionof the type of the channel and the coding technique used. In Gaussianchannels, the error distribution cannot be changed by relocating thebits, so interleaving is not useful. Frequency and time interleaving arethe most common forms of interleaving.

Frequency interleaving is used to exploit the frequency diversity inwide-band transmissions. After frequency interleaving, the local deepfading is averaged over the whole bandwidth of the system. Frequencyinterleaving should be implemented for all the data symbols in a singleOFDM symbol. This means, that the data symbols of two neighboring OFDMsymbols should not be interleaved in one iteration. For this reason, thedimension of a conventional frequency interleaver is equal to the numberof data symbols in a single OFDM symbol i.e. number of tones (K)×numberof bits/tone (B). Frequency Interleaving is used in IEEE 802.11astandard, where the depth has obeen defined to be equal to one OFDMsymbol providing an important improvement of the system. The combinedeffect of interleaving and convolution channel coding takes advantage ofthe frequency diversity provided by the wideband nature of thetransmitted signal.

Time interleaving is used to exploit the time diversity of the channel.After time interleaving, the local time deep fading in some OFDM symbolsis averaged over all OFDM symbols. The time interleaving depth should belarger than the maximum burst-error in the time domain. Timeinterleaving is usually not applied in WLAN systems, because of theslowly fading characteristics of the channel.

Antenna technology used in a wireless transmission system can becategorized into four broad categories. FIG. 1A shows a Single InputSingle Output (SISO) transmission system. SISO refers to a wirelesscommunications system in which one antenna is used at the source i.e.the transmitter 100 and one antenna is used at the destination i.e. thereceiver 102. In some environments, SISO systems are vulnerable toproblems caused by multipath effects such as fading, cut-out andintermittent reception. SISO systems have only one antenna and cantransmit and receive only one stream of data thereby suffering frommultipath effects.

In order to minimize or eliminate problems caused by multipath wavepropagation, smart antenna technology is used. A smart antenna is adigital wireless communications antenna system that takes advantage ofdiversity effect at the source (transmitter), the destination(receiver), or both. Diversity effect involves the transmission and/orreception of multiple radio frequency (RF) waves or multiple datastreams to increase data speed and reduce the error rate. The next threecategories in antenna technology belong to the smart antenna arena andhave been introduced above as SIMO, MISO and MIMO.

FIG. 1B shows a SIMO transmitter 104 and receiver 106. In SIMO systems asingle antenna is used at the transmitter 104 and multiple antennas areused at the receiver 106. The output of the antennas are combined tominimize errors and optimize data speed. The transmitter 104 has onlyone antenna thereby allowing transmission of only one data stream, whilethe receiver 106 can receive multiple data streams. SIMO technology haswidespread applications in DTV, WLANs, MANs and mobile communicationsamong others. An early form of SIMO, known as diversity reception, hasbeen used by military, commercial, amateur, and shortwave radiooperators at frequencies below 30 MHz since the First World War.

FIG. 1C shows a MISO transmitter 108 and receiver 110. MISO is anantenna technology for wireless communications in which multipleantennas are used at the transmitter 108. The output of the antennas arecombined to minimize errors and optimize data speed. MISO technologyallows transmission of multiple data streams at the transmitter 108 butwill allow only single data stream reception at the receiver 110. MISOtechnology also has widespread applications in DTV, WLANs, MANs andmobile communications among others.

FIG. 1D shows a MIMO transmitter 112 and receiver 114. MIMO systems area promising new way of more fully utilizing the spatial dimension of achannel by employing multiple antennas at both the transmitter 112 andthe receiver 114. As used herein, channel refers to an availablefrequency spectrum. MIMO systems have been shown to support much higherdata rates than traditional single antenna systems while using the sameamount of bandwidth or channel. This increase is achieved by takingadvantage of the multiple paths that most signals take between thetransmitter and the receiver, rather than suffering from it. MIMOtechnology allows multiple data stream transmission at the transmitter112 and also allows multiple data stream reception at the receiver 114.

In order to increase reliability, data bits are spread in frequencyand/or position. FIG. 2. is a frequency diagram of a channel offrequencies or tones, modulated with bit pairs 200 and 202, 204 and 206,208 and 210. The X-axis represents frequency and the Y-axis representsthe SNR. Bits 200, 202, 208, and 210 are spaced by a first interleavingscheme that places adjacent bits near the same tone or frequency. Inother words, adjacent bits have not been separated across position orfrequency. This is generally undesirable because if the tone is subjectto interference, related bits will likely both be lost. For example,adjacent bits 208 and 210 have been placed near the same tone in a partof the signal having a very low SNR. Thus, if that part of the signal islost due to interference, adjacent bits 208 and 210 cannot be recoveredbecause during error correction at the receiver, at least one bit of anadjacent bit pair is required to recover a lost signal.

Adjacent bits 204 and 206, on the other hand, have been spaced apartfrom one another by position and multiple tones or frequencies. As aresult, the probability of both bits being lost during transmission isthereby significantly reduced.

However with multiple antennas as in MIMO systems, multiple data streamscan be transmitted and hence we require an interleaver that can spreadbits across frequencies, streams and in position thereby increasingtransmission reliability. Furthermore, to reduce transmission latency,the bits should be interleaved across a single symbol period instead ofmultiple symbol periods.

In accordance with an embodiment of the invention, data streams areinterleaved across space, as well as frequency and position. In otherwords, adjacent data bits are spread across multiple transmit streams orpaths. The data bits are optionally transmitted within a given symbolperiod over the multiple paths. Spreading the bits across multipletransmit streams can prevent long runs of low reliability (LSB) bits.

FIG. 3. is an example graph of data bits 202-210, interleaved acrossmultiple transmit data streams 302, 304, and 306. The X-axis representsfrequency, the Y-axis represents the SNR and the Z-axis represents thestreams of data.

In accordance with an aspect of the invention, a novel interleavingscheme is provided that more fully utilizes the available channel anddata paths.

FIG. 4 is block diagram of an example communication system. FIG. 4including a transmit portion 420 and a receive portion 422. The transmitportion 420 receives a bit stream 400 that is to be transmitted. Thetransmit portion 420 includes an encoder 402, an interleaver 404, amodulator 406, and a transmitter 408. The receive portion 422 includes areceiver 410, a demodulator 412, a de-interleaver 414, and a decoder416. The receive portion 422 outputs a decoded data 418.

The encoder 402 encodes the bit stream 400 into a form that isacceptable for transmission. This is usually done by implementing analgorithm. The interleaver 404 randomizes the encoded bits received fromthe encoder 402, so that error events due to deep channel fades aremaximally de-correlated.

The modulator 406 encodes the interleaved bits on a carrier signal whichis typically a sine-wave signal. Modulation techniques include but arenot limited to Phase Modulation (which includes Binary Phase ShiftKeying (BPSK), Quarternary Phase Shift Keying (QPSK)), Single-Sidebandmodulation (SSB), Vestigial-Sideband modulation (VSB, or VSB-AM),Quadrature Amplitude Modulation (QAM), OFDM, also known as Discretemultitone modulation (DMT), Wavelet modulation, Trellis modulation,Adaptive modulation and Sigma-delta modulation (ΣΔ).

The transmitter 408, in conjunction with a transmit antenna, propagatesthe modulated signal such as radio, television, or othertelecommunications. The transmitter 408 typically includes a powersupply, an oscillator, and amplifiers for audio frequency (AF),intermediate frequency (IF) and radio frequency (RF) depending upon thetype of transmission.

The receiver 410, in conjunction with a receive antenna, receives thetransmitted wireless signal from the transmitter 408 and converts it toa suitable format for the next processing stage i.e. the demodulator412. The demodulator 412 recovers the information content from thecarrier wave of the signal recovered by the receiver 410. Thede-interleaver 414 recovers the randomized encoded bits received fromthe de-modulator.

The de-interleaver 414 needs to be synchronized with the interleaver404. This can be performed by inserting a periodic unique sequence(unique word) after interleaving. This unique word is detected at thereceiver to recover the start of frame synchronization. The unique wordis generally not subjected to interleaving.

The decoder 416 reverses the encoding performed by the encoder 402 sothat the original information can be retrieved.

Methods and systems for interleaving are now described.

FIG. 5 shows bits interleaved by a conventional 802.11a QPSK interleaver500. The QPSK interleaver 500 receives an encoded bitstream b_(k) fromthe encoder 402. The bits in the bit stream b_(k) are in their encodedorder 502. The QPSK interleaver 500 randomizes the bitstream b_(k) toproduce the interleaved bit stream b_(i). The formula used to randomizethe bitsteam b_(k) is defined as: $\begin{matrix}{{i = {{{6\left( {k\quad{mod}\quad r} \right)} + {\left\lfloor \frac{k}{r} \right\rfloor\quad{where}\quad k}} = 0}},1,{2\ldots\quad 47}} & (1)\end{matrix}$Where,

-   -   i is the position where the k^(th) bit should be placed,    -   k is the bit index, and    -   r is the number of columns in the interleaver.

In an example where r=16, bit 0 is placed in position 0, bit 1 is placedin the 6^(th) position and bit 16 is placed in the 1^(st) position etcetera.

The interleaved bits 504 are then grouped and transmitted on separatetones to improve transmission reliability as explained above. Bits b₀and b₁₆ are transmitted on tone 0, bits b₃₂ and b₄₈ on tone 1, bits b₆₄and b₈₀ on tone 2 and bits b₁ and b₁₇ on tone 3. Thus, the QPSKinterleaver 500 separates adjacent bits b₀ and b₁ by at least 3 tones asshown in FIG. 5. The QPSK interleaver 500 separates adjacent bits inposition and frequency. The size of the legacy QPSK interleaver 500 isdefined as:N _(CBPS) =B*KWhere,

-   -   N_(CBPS) is the number of coded bits per symbol    -   B is the number of bits/tone and    -   K is the number of tones.

For example, in FIG. 5, B=2 and K=48. The size of the QPSK interleaver500 is therefore 96 bits.

FIG. 6 shows bits interleaved by a 16 QAM interleaver across 48 tones.As seen in FIG. 6, adjacent bits bit 0 and bit 1 are transmitted onseparate tones. Bit 0 is transmitted on tone 1 and bit 1 is transmittedon tone 4 allowing a 3 tone separation between the bits and therebyproviding better protection to adjacent bits. Thus for example if thefirst three tones experience a fade, only bits 0, 64 and 128 will belost. Since their adjacent bits 1, 65 and 129 are on separate tones(with at least 3 tone separation), there is a high probability thatthese bits will be received and can be used to recover the lost bits 0,64 and 128 by the error correction scheme used at the transceiver.

The interleaving schemes shown in FIGS. 5 and 6 interleave bits inposition and frequency, as shown in FIG. 2. With a MIMO system providingmultiple transmitter 112 and receiver 114 antennas, bits can beinterleaved across frequency, postion and space as shown in FIG. 3. Inan embodiment, adjacent bits are spread across only one symbol periodinstead of multiple symbol periods as is done by conventionalinterleavers.

FIG. 7 is an exemplary embodiment of the interleaver 404 that spreadsbits over one symbol period and across streams, frequency and position.FIG. 7 shows encoded bits 700, a row-column interleaver 702, a M-ary bitmapper 704, a block converter 706, a block rotator 708 and interleavedbits 710. Encoded bits b₀ to b_(BKN-1) 700 are bits recevied from theencoder 402. The encoded bit stream b_(k) is processed by the row-columnbit interleaver 702. The row column interleaver 702 writes the encodedbit stream b_(k) row by row and reads them out column by column. Anembodiment of the row column interleaver 702 according to the inventionand the permutations performed on bit stream b_(k) will be discussed ingreater detail later in the application. The result from the row columninterleaver 702 is bit stream b_(j) which is fed into a M-ary mapper704, that groups N_(BPSC) (number of bits per sub-carrier) bits togetherto produce M-ary subsymbols c_(l). The permutations performed on bitstream b_(j), where the number of streams is N_(SS), are defined as:c _(l) =[b _(lB) b _(lB+1) . . . b _(lB+B-1)], where l=0, 1, . . . , N_(ss) K−1  (2)

Next, the M-ary subsbymbols c_(l) are further grouped into a number ofstreams (N_(SS))×t groups, each group having K/t subsymbols to produceblocks g_(p) where t is a block rotation parameter and a function of thenumber of tones K. For example, if N_(SS)=2, t=K; for N_(SS)=3, t=K andfor N_(SS)=4, t=K/2. The values for all parameters described herein areexample embodiments and should in no way limit the parameters to thesevalues.

The permutations performed on subsymbols c_(l) are defined by:$\begin{matrix}{{g_{p} = \left\lfloor {c_{p\frac{\kappa}{t}}c_{{p\frac{\kappa}{t}} + 1}\ldots\quad c_{{p\frac{\kappa}{t}} + \frac{\kappa}{t} - 1}} \right\rfloor},\quad{{{where}\quad p} = 0},1,\ldots\quad,{{N_{ss}t} - 1}} & (3)\end{matrix}$

Lastly the blocks g_(p) are rotated by the block rotator 708 tointroduce greater separation between adjacent bits and produce the astream of block o_(p). The permutations used to produce block streamo_(p) are governed by the number of streams in use. The permutationsperformed on block stream g_(p) for two transmit streams are defined as:$\begin{matrix}{o_{p} = \begin{Bmatrix}{g_{p},\quad{{{where}\quad p} = 0},2,\ldots\quad,{{N_{SS}t} - 2}} \\{g_{{({p + t})}{mod}\quad N_{SS}t},\quad{{{where}\quad p} = 1},3,{{\ldots\quad N_{SS}t} - 1}}\end{Bmatrix}} & (4)\end{matrix}$

The permutations performed on block stream g_(p) for three transmitstreams are defined as: $\begin{matrix}{o_{p} = \begin{Bmatrix}{g_{p},\quad{{{where}\quad p} = 0},2,4,6,\ldots\quad,{{N_{SS}t} - 2}} \\{g_{{({p + t})}{mod}\quad N_{SS}t},\quad{{{where}\quad p} = 1},5,9,\ldots\quad,{{N_{SS}t} - 3}} \\{g_{{({p + {2t}})}{mod}\quad N_{SS}t},\quad{{{where}\quad p} = 3},7,11,\ldots\quad,{{N_{SS}t} - 1}}\end{Bmatrix}} & (5)\end{matrix}$

The permutations performed on block stream g_(p) for four transmitstreams are defined as: $\begin{matrix}{o_{p} = \begin{Bmatrix}{g_{p},\quad{{{where}\quad p} = 0},4,8,\ldots\quad,{{N_{SS}\quad t}\quad - \quad 4}} \\{g_{{({p + t})}{mod}\quad N_{SS}t},\quad{{{where}\quad p} = 1},5,9,\ldots\quad,{{N_{SS}t} - 3}} \\{g_{{({p + {2t}})}{mod}\quad N_{SS}t},\quad{{{where}\quad p} = 2},6,10,\ldots\quad,{{N_{SS}t} - 2}} \\{g_{{({p + {3t}})}{mod}\quad N_{SS}t},\quad{{{where}\quad p} = 3},7,11,\ldots\quad,{{N_{SS}t} - 1}}\end{Bmatrix}} & (6)\end{matrix}$

Interleaved bits b₀ to b_(NKB-1) 710 show how the bits within the blockstream o_(p) have been separated by position, frequency (tones) andspace (streams). In this example bits b₀ to b_(B-1) are on tone 0 andbits b_((k-1)B) to b_(KB-1) are on tone K-1. There are K tones (0 toK-1) and bits b₀ to b_(KB-1) on stream 0. The remaining bits b_(KB) tob_(NKB-1) are repeatedly divided amongst K tones and are on separatestreams with b_(NKB-1) being bit B of tone K of stream N_(SS). Theencoded bit stream 700 has now been interleaved 712 across frequency,position, space and spread over one symbol period for transmission frommultiple antennas.

FIG. 8 shows the row-column interleaver 702 matrix according to anembodiment of the present invention. The size of the row-columninterleaver is given by:N′ _(CBPS) =N _(SS) ×K×B

-   -   where    -   N′_(CBPS) is the number of coded bits per symbol    -   N_(SS) is the number of streams    -   K is the number of tones/stream    -   and B is the number of bits/tone

The row-column interleaver 702 has r columns and N′_(CBPS)/r rows. Thebit stream b_(k) is written row-by-row and read out column-by-column asbit stream b_(j). The reverse process is performed at the de-interleaver414 to recover the original order of the transmitted bits. Therow-column interleaver 702 is defined by a two-step permutation. In theequations below, k denotes the index of the bit before the firstpermutation, i denotes the index after the first but before the secondpermutation, j denotes the index after the second permutation andN′_(CBPS) is the total number of bits to be transmitted. The twopermutations are given by: $\begin{matrix}{{{i = {{\frac{N_{CBPS}^{\prime}}{r}\left( {k\quad{mod}\quad r} \right)} + \left\lfloor \frac{k}{r} \right\rfloor}}\quad,{{{where}\quad k} = 0},1,{{\ldots\quad N_{CBPS}^{\prime}} - 1}}{and}} & (7) \\{{j = {{s\left\lfloor \frac{i}{s} \right\rfloor} + {\left( {i + N_{CBPS}^{\prime} - \left\lfloor \frac{ri}{N_{CBPS}^{\prime}} \right\rfloor} \right){mod}\quad s}}},{{{where}\quad i} = 0},1,{{\ldots\quad N_{CBPS}^{\prime}}\quad - \quad 1}} & (8)\end{matrix}$

The first permutation ensures that adjacent bits are mapped ontononadjacent tones and non-adjacent streams. The second permutationensures that adjacent bits are mapped alternately onto less and moresignificant bits of the constellation, thereby avoiding long runs of lowreliability (LSB) bits. The number of columns (r) is a design parameterthat can be varied. However, r between 17 and 47 yields the best resultsfor interleaving the bits across frequency, space and position. In anembodiment of the invention, r=24 yields optimal results. In legacy SISOdevices, a typical value for r is 16.

FIG. 9 shows the interleaved result produced by an embodiment of theinvention. FIG. 9 shows bits interleaved in pairs of B=2 bits/tone,across K=108 tones/stream and N_(SS)=2 streams. The first row 900 haspaired bits that are transmitted on stream 1 and the second row 902 haspaired bits that are transmitted on stream 2. The size of the row-columninterleaver used to produce the results in FIG. 9 isN′_(CBPS)=N_(SS)×K×B=2×48×2=432 bits. The interleaver 404 used togenerate these results has r=24 columns as a design parameter in therow-column matrix 702. The design parameter of 24 columns when used with108 tones with 2 bits/tone leads to at least four tone and one streamseparation between adjacent bits. As can been in FIG. 9, bits b₀ and b₁have at least a four tone and one stream separation between them and areplaced on alternate streams. Adjacent bits are also mapped alternatelyonto less and more significant bits of the constellation and therebylong runs of low reliability (LSB) bits are avoided.

FIG. 10 is another example of the interleaved result produced by anembodiment of the invention. FIG. 10 shows bits interleaved in pairs ofB=2 bits/tone, across K=108 tones and N_(SS)=3 streams. The first row1000 has paired bits that are transmitted on stream 1, the second row1002 has paired bits that are transmitted on stream 2 and the third row1004 has paired bits that are transmitted on stream 3. The size of therow-column interleaver used to generate these results isN′_(CBPS)=N_(SS)×K×B=2×48×3=648 bits. The interleaver 404 used togenerate these results has r=24 columns as a design parameter in therow-column matrix 702. The design parameter of 24 columns when used with108 tones with 2 bits/tone leads to at least four tone and one streamseparation between adjacent bits. As can been in FIG. 10, adjacent bitsbo and b, have at least a four tone and one stream separation betweenthem and are placed on alternate streams. Adjacent coded bits are alsomapped alternately onto less and more significant bits of theconstellation and thereby long runs of low reliability (LSB) bits areavoided.

The embodiments presented above are described in relation to MIMOsystems and wireless communications. The invention is not, however,limited to MIMO and wireless communications. Based on the descriptionherein, a person skilled in the relevant art(s) will understand that theinvention can be applied to other applications

As used herein, the terms “tone”, “frequency”, “sub-carrier” and theirplural forms are used throughout the application to denote frequenciesused to transmit bits and are interchangeable with the term “frequency”as is apparent to any person skilled in the relevant art(s).

The invention has been described for transmission systems having two orthree antennas and/or two or three transmission streams. The inventionis not, however, limited to these example embodiments. Based on thedescription herein, one skilled in the relevant art(s) will understandthat the invention can be applied in systems with four or more transmitantennas or a single antenna capable of transmitting multiple streams.

The present invention, or portions thereof, can be implemented inhardware, firmware, software, and/or combinations thereof. Consequently,the invention may be implemented in the environment of a computer systemor other processing system. An example of such a computer system 1100 isshown in FIG. 6. The computer system 1100 includes one or moreprocessors, such as processor 1104. Processor 1104 can be a specialpurpose or a general purpose digital signal processor. The processor1104 is connected to a communication infrastructure 1106 (for example, abus or network). Various software implementations are described in termsof this exemplary computer system. After reading this description, itwill become apparent to a person skilled in the relevant art how toimplement the invention using other computer systems and/or computerarchitectures.

Computer system 1100 also includes a main memory 1105, preferably randomaccess memory (RAM), and may also include a secondary memory 110. Thesecondary memory 110 may include, for example, a hard disk drive 1112,and/or a RAID array 1116, and/or a removable storage drive 1114,representing a floppy disk drive, a magnetic tape drive, an optical diskdrive, etc. The removable storage drive 1114 reads from and/or writes toa removable storage unit 1118 in a well known manner. Removable storageunit 1118, represents a floppy disk, magnetic tape, optical disk, etc.As will be appreciated, the removable storage unit 1118 includes acomputer usable storage medium having stored therein computer softwareand/or data.

In alternative implementations, secondary memory 1110 may include othersimilar means for allowing computer programs or other instructions to beloaded into computer system 1100. Such means may include, for example, aremovable storage unit 1122 and an interface 1120. Examples of suchmeans may include a program cartridge and cartridge interface (such asthat found in video game devices), a removable memory chip (such as anEPROM, or PROM) and associated socket, and other removable storage units1122 and interfaces 1120 which allow software and data to be transferredfrom the removable storage unit 1122 to computer system 1100.

Computer system 1100 may also include a communications interface 1124.Communications interface 1124 allows software and data to be transferredbetween computer system 1100 and external devices. Examples ofcommunications interface 1124 may include a modem, a network interface(such as an Ethernet card), a communications port, a PCMCIA slot andcard, etc. Software and data transferred via communications interface1124 are in the form of signals 1128 which may be electronic,electromagnetic, optical or other signals capable of being received bycommunications interface 1124. These signals 1128 are provided tocommunications interface 1124 via a communications path 1126.Communications path 1126 carries signals 1128 and may be implementedusing wire or cable, fiber optics, a phone line, a cellular phone link,an RF link and other communications channels.

The terms “computer program medium” and “computer usable medium” areused herein to generally refer to media such as removable storage drive1114, a hard disk installed in hard disk drive 1112, and signals 1128.These computer program products are means for providing software tocomputer system 1100.

Computer programs (also called computer control logic) are stored inmain memory 1108 and/or secondary memory 110. Computer programs may alsobe received via communications interface 1124. Such computer programs,when executed, enable the computer system 1100 to implement the presentinvention as discussed herein. In particular, the computer programs,when executed, enable the processor 1104 to implement the processes ofthe present invention. Where the invention is implemented usingsoftware, the software may be stored in a computer program product andloaded into computer system 1100 using raid array 1116, removablestorage drive 1114, hard drive 1112 or communications interface 1124.

In another embodiment, features of the invention are implementedprimarily in hardware using, for example, hardware components such asApplication Specific Integrated Circuits (ASICs) and gate arrays.Implementation of a hardware state machine so as to perform thefuictions described herein will also be apparent to persons skilled inthe relevant art(s).

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample, and not limitation. It will be apparent to persons skilled inthe relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.

The present invention has been described above with the aid offunctional building blocks and method steps illustrating the performanceof specified functions and relationships thereof. The boundaries ofthese functional building blocks and method steps have been arbitrarilydefined herein for the convenience of the description. Alternateboundaries can be defined so long as the specified functions andrelationships thereof are appropriately performed. Any such alternateboundaries are thus within the scope and spirit of the claimedinvention. One skilled in the art will recognize that these functionalbuilding blocks can be implemented by discrete components, applicationspecific integrated circuits, processors executing appropriate softwareand the like or any combination thereof. Thus, the breadth and scope ofthe present invention should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with the following claims and their equivalents.

1. A method to process transmission data comprising: a) receiving bits; b) writing said received bits row-by-row in a matrix; c) reading said bits written row-by-row in said matrix column-by-column; d) grouping a pre-determined number of said bits read column-by-column to form subsymbols; e) grouping said subsymbols to form groups of subsymbols; f) rotating said groups of subsymbols; g) transmitting said subsymbols over transmit paths; wherein adjacent bits received in step a) are separated over frequency, position, and space.
 2. The method of claim 1, wherein adjacent bits received in step a) are separated over frequency, position, and streams, and over one symbol period
 3. The method of claim 1, wherein a size of said matrix (N′_(CBPS)) is defined as: N′_(CBPS)=N_(SS)×K×B; wherein, N_(SS) is the number of streams; K is the number of tones/stream and B is the number of bits/tone.
 4. The method of claim 1, wherein a number of columns (r) in said matrix is greater than or equal to 17 and less than or equal to
 47. 5. The method of claim 1, wherein a number of columns (r) in said matrix is
 24. 6. The method of claim 1, further comprising mapping adjacent received bits onto nonadjacent tones and non-adjacent streams using a first permutation.
 7. The method of claim 6, further comprising mapping adjacent received bits alternately onto less and more significant bits of a constellation using a second permutation.
 8. The method of claim 7, wherein said first permutation is defined as: ${i = {{{\frac{N_{CBPS}^{\prime}}{r}\left( {k\quad{mod}\quad r} \right)} + {\left\lfloor \frac{k}{r} \right\rfloor\quad{where}\quad k}} = 0}},1,{{{\ldots\quad N_{CBPS}^{\prime}} - 1};}$ and said second permutation is defined as: $j = {{s\left\lfloor \frac{i}{s} \right\rfloor} + {\left( {i + N_{CBPS}^{\prime} - \left\lfloor \frac{ri}{N_{CBPS}^{\prime}} \right\rfloor} \right){mod}\quad s}}$ where  i = 0, 1…  N_(  CBPS)^(  ′)  −  1; wherein, k denotes the index of the bit before the first permutation; i denotes the index after the first but before the second permutation; j denotes the index after the second permutation; and N′_(CBPS) is the number of coded bits per sub carrier.
 9. The method of claim 1, further comprising introducing at least four tones and one stream separation between adjacent bits received in step a) and transmitted in step g).
 10. The method of claim 1, further comprising placing successive modulated points on alternate streams.
 11. The method of claim 1, wherein in step d) said pre-determined number of bits is the number of bits per tone.
 12. The method of claim 1, wherein rotating said group of sub-symbols in step f) increases separation between adjacent bits.
 13. A system to process transmission data comprising: a) means for receiving bits; b) means for writing said received bits row-by-row in a matrix; c) means for reading said bits written row-by-row in said matrix column-by-column; d) means for grouping a pre-determined number of said bits read column-by-column to form subsymbols; e) means for grouping said subsymbols to form groups of sub symbols; f) means rotating said groups of subsymbols; g) means for transmitting said subsymbols over transmit paths; wherein adjacent bits received in step a) are separated over frequency, position, and space.
 14. The system of claim 13, wherein adjacent bits received in step a) are separated over frequency, position, and streams, and over one symbol period
 15. The system of claim 13, wherein a size of said matrix (N′_(CBPS)) is defined as: N′_(CBPS)=N_(SS)×K×B; wherein, N_(SS) is the number of streams; K is the number of tones/stream and B is the number of bits/tone.
 16. The system of claim 13, wherein a number of columns (r) in said matrix is greater than or equal to 17 and less than or equal to
 47. 17. The system of claim 13, wherein a number of columns (r) in said matrix is
 24. 18. The system of claim 13, further comprising means for introducing at least four tones and one stream separation between adjacent bits received in step a) and transmitted in step g).
 19. A system to process transmission data comprising: a) a module to receive bits; b) a module to write said received bits row-by-row in a matrix; c) a module to read said bits written row-by-row in said matrix column-by-column; d) a module to group a pre-determined number of said bits read column-by-column to form subsymbols; e) a module to group said subsymbols to form groups of subsymbols; f) a module to rotate said groups of subsyrnbols; g) a module to transmit said subsymbols over transmit paths; wherein adjacent bits received in step a) are separated over frequency, position, and space.
 20. The system of claim 19, wherein adjacent bits received in step a) are separated over frequency, position, and streams, and over one symbol period. 